Magnetron



July 16, 1946- R. J. BONDLEY MAGNETRON Filed Dec. 24, 1942lll/1111111111111 Ill lll VIII/ Inventor: Ralph J. Bondley. by .if/w1? MHi Attorney.

Patented July 16, 1946 MAGNETRON v Ralph J. BondIey, Scotia, N. Y.,assignor to General Electric Company, a corporation of New YorkApplication December 24, 1942, Serial No. 470,041

, l My invention relates to high frequency electric discharge devicesand more particularly to ultra high frequency magnetronsof the spaceresonant type- In the development of ultra high frequency electricdischarge devices, and particularly in the effort to increase theoperating frequency of discharge devices of this nature, the incidentdecrease in the dimensions of the cooperating electrodes and associatedstructure has entailed certain limitations as to the magnitude ofvoltages which may be used in the higher frequency devices. Inaccordance with the teachings of my invention described hereinafter, Iprovide a new and improved structure for an electric discharge device ofthe magnetron type wherein the operating'frequency may be substantiallyincreased, and wherein the structure is arranged and .positioned so thata reduction in the operating voltage of the device is not required. l

It is an object of my invention: to provide a new and improved ultra,high frequency electric f* discharge device.

It is another object of my'invention to provide a new and improved ultrahigh frequency electric discharge device of the magnetron type.

It is a further object of `my invention to provide a new and improvedultra vhigh `frequency magnetron wherein the cathode structure may besupported centrally with respect to Va magnetic pole piece, and whereinthe magnetic iield distortion is reduced or substantially eliminated.

It is a still further object of my invention to provide a new andimproved structure for an ultra high frequency electric discharge deviceof the magnetron type wherein the relative dimensions of the cathodestructure and the magnetic pole piece obtain a desired configuration ofthe magnetic lines of force within the space discharge region, therebyproducing a focusing eiect upon the electrons constituting the spacedischarge or limiting the divergence of the electrons at the ends of thespace discharge region.

Brieiiy stated, in the illustrated embodiment of my invention I providea new and improved ultra high frequency magnetron wherein a cathode issupported centrally with respect to a longitudinal magnetic pole pieceby means of cathode supporting structure extending through alongitudinal channel in the pole piece. Magnetic field distortion isreduced, or substantially eliminated, or controlled in configuration bythe provision of a restricted opening in the channel. at the magneticpole 1piece face. In this manner, the relative dimensions of the cathodeand the magnetic pole piece may be employed to obtain a magnetic fieldin which the magnetic linesk of force are substantially parallel withinthe space discharge region, or the relative dimensions may be chosen toproduce a barrelingg effect which tends `to 9 Claims. (Cl. Z50-27.5)

focus the `electrons of the space discharge at the For a betterunderstanding of my invention,v

reference may be had tothe following description taken in connectionwith the accompanying v drawing, and its scope will be pointed out inthe appended claims.

Fig. 1 illustrates in cross sectional View an ernbodiment of myinvention as applied to an ultra high frequency magnetron of the typedisclosed and broadly claimed in a copending patent application SerialNo. 447,903 of Elmer D. McArthur, led June 22, 1942 and which isassigned to the assignee of the present application. Fig. 2 is a crosssectional plan view of the anode structure.

Referring now to Fig. 1 of VtheA accompanying drawing, I have thereillustrated my invention as applied to an electric discharge device,such as an ultra high frequency magnetron, including an elongatedcylindrical container the lateral wall structure of which is provided bya single metallic tube I which consists of a ferro-magnetic materialsuchas cold rolled steel, or the like. The ends of the container or tubeI are closed by flanged v members 2 and 3 which are welded or otherwisehermetically sealed to the inner surface of tube l.

Within the container and approximately at its central portion there isprovided an anode structure 4 shown in detail plan View in Fig. 2. Theanode structure 4 is -preferab-ly of circular configuration providedwith an enlarged central opening 5 and a plurality or series of smalleropenings l arranged symmetrically about the central opening. The centralopening 5 is joined to the openings 6 by means of radially extendingslots 1.

The anode structure 4, which may preferably consist of copper, issupported by being brazed to the inner surface of tube l. Within theopenv ing 5 of thevanode structurethere is provided a thermioniccylindrical cathode which may be of the indirectly heated typecomprising a metallic sleeve or cylinder 8 of nickel or molybdenum whichis coated externally with a suitable activating `material, such asbarium oxide. Within the cylinder v there is provided a filamentarycathode heating element 9 by which the lcathode is maintained at anemissive temperature.

In operating the device, a space discharge is assumed to be developed inthe region defined between the cathode cylinder 8 and the surroundinganode structure i by application of a suitable potential between theanode structure and the cathode. rlhe electrons which compose this spacecharge are given a spiral or orbital motion by a magnetic field producedby means 4to be described presently,. and the resultant electronoscillation, or oscillations, about the cathode produce excitation ofthe anode structure at its resonantl frequency or Vharmonics thereof,VThe anode structure may be considered as consisting of a plurality ofmutually coupled units in each of which the inductance is provided bythewall sur- Vface of openings 6 andthe capacitance is pro-` of themagnetized pole pieces,these members may be constructed of a suitablemetal or alloy having high coercive force anda high energy factonsuch ias alloys, or groups of alloys,'of aluminum, nickel and cobalt.

In order to provide relatively low reluctance g connections betweenv thebase extremities of the respective pole pieces It) and Il, the polepieces may be seated upon relatively thick disk-like members l2 and 1 3constructed of a ferromagnetic material, such as steel. VThese membersare l providedwith slots I 4 and l5 in order to afford suitable passagesfor the evacuation of the discharge device. Passage I5 is incommunication with an opening. I3 inanged part 3, 'and a suitableYtubulation l1 may be employed for sealing the discharge device structureafter'evacuation:

To secure the pole pieces IU and l l rmly t0 the base members, use maybe made of clamping rings' I3 andlV which are slipped overthe polepieces and welded to the base members. Accurate spacing of pole piecesvIt'l and l l with reference to the anodeY structure may be obtained bythe use of spacing rings and 2l used in the manner illustrated. As shownin Fig. 1, each of` these rings is interposed between one surface ofjanode structure 4 anda surface of apertured disks 22 and `23,'each diskin turn being in abutment, with anrappropriately formed shoulder provideby the adjacent pole pieces.

As a means for supporting the cathode struc-` ture centrally withrespect to the anode structure* 4, Imay'employ a concentric cableconstruction broadly disclosed and claimed in my copending` patentapplication rSerial No. 465,424, led No- V vember ,13, 1942, and whichis assigned to theassignee of the 'present'application Referringvmorespecically to Fig.'l of 'the drawing, I provide a concentric cableconstruction which ex-V tends ;through a longitudinal channel 24 in themagnetic pole piece l0. This channel is prefer` ably circular in crosssection and is provided with,`

a restricted section 25 in the vicinity of the pole face 26. Thediameter of the channel Vopening in the vicinity of section 25 ispreferably equal to or 8 and the opposite or cooperating face of theanode structure 4. l For example, by choosing the relative dimensions cfthe restricted opening at 25 and the cathode diameter, thefmagnetic eldmay be con;` trolledso that the magnetic lines of force within ythespace'dlscharge region are substantially parallel. Furthermore, therelative dimensions may be chosen so that the magnetic lines Of fOrCe alless than the diameter of the cathode cylinder 8. By the choice of therelative dimensions of the` having a pole face substantially parallel toan Within the space discharge region tend to barrel outwardly, therebyexerting afocusing effect on A l the electrons constituting the spacedischarge and minimizing the divergence of the electrons at the top andbottom of the space discharge'region, In either instance, that is bymaintaining the magnetic field lines of force substantially parallel orby producing the outward barreling effect, the divergence of theelectrons at the ends of the space discharge region is minimized.

Considering more particularly the cathode supporting structure, Iprovide a concentric cable construction including an outer tubularmetallic conductor 21, an inner conductor 28 and an interspaced tubularinsulator 23, conductors 21 and 2 8 being connectedto externallyaccessible lead-inv wires 3i) and 3l Whichare sealed by means of anysuitable sealing structure, such as a anged me-Y ductor 21 so that thedevice may be operatedY at substantially high voltages. y .f

The cathode structure is supported by the concentric cable constructionthrough a'anged and apertured collar 36 which is attached to a metallicdisk 31, the vlatter of which is kprovided with a il' plurality ofmetallic tabs `.which are welded or soldered to cathode cylinder 8. Oneterminal of f the lamentarycathode heating element 9 is connected to theinner conductor 28, and the other terminal is connected to the outerconductor 21 by being connected to the cathode cylinder 8. `Of course,it is to be appreciated that the upper ter'- minal of the cathodeheating element 9 which is connected to the inner conductor 28 isdisplaced from and electrically insulated'from the collar 35 and disk31.Y Y

Energy may be extracted from the discharge device by employing asuitable output electrode means, such as a loop 38 which extends intoone of the openings 6 and which constitutes an extension of an innerconductor 3B comprising one part of a concentric cable constructioncomprise ing conductor 39 and an outer tubular conduce tor'40.1

While I have shown and described my inven tion as applied to aparticular device andv as em-V bodying various elements,'it will beobvious to those skilled in the art that changes and mcdications may bev'made `without departing from` my invention, and I, therefore, aim inthe ap pended claims to cover all such changesr and modications as fallVWithin the true spirit and electrodes including a cathode and an anodestructure lsubstantially surrounding Said cathode and having Vopposedend faces, means for estab- 'Y lishing a magnetic eld comprising a polepiece end face of said anodev structure, said pole piece having alongitudinal channel extending therethrough and terminate'din the planeof said pole face, cathode supporting structure extending netron typecomprising a plurality of enclosed` electrodes including a cylindricalcathode and an anode structure substantially surrounding said cathodeand having opposed end faces, means for establishing a magnetic fieldcomprising a pole piece having a pole face substantially parallel to anend face of said anode structure, said pole piece having therein alongitudinal channel extending through said iield piece and terminatedat the face thereof in a restricted portion the dimension of which isequal to or less than the diameter of said cathode, and means extendingthrough said channel supporting said cathode.

3. An electric discharge device of the mag- `netron type comprising aplurality of enclosed electrodes including a Vcylindrical cathode and anannular anode structure substantially surrounding said cathode, meansfor establishing a magnetic field comprising a pole piece having a poleface positioned near said anode structure and having therein alongitudinally extending channel terminated at the face, said channelhaving a restricted section of a dimension substantially less than thetransverse dimension of said cathode to minimize the magnetic fielddistribution, and means extending through said channel supporting saidcathode.

4. An electric discharge device of the magnetron type comprising aplurality of enclosed electrodes including a cathode having an emittingsurface and an anode structure substantially surrounding said cathodeand having opposed end faces, means for establishing a magnetic eldcomprising a pole piece yhaving a pole face substantially parallel to anend face of said anode structure, said pole piece having therein alongitudinally extending channel terminated at the face thereof in arestricted section, the dimension of said section being equal to or lessthan the transverse dimension of the emitting surface of said cathode sothat the magnetic eld tends to focus the electrons constituting thespace discharge between said cathode and said anode structure at theends of the space discharge region, and means extending through saidchannel for supporting Isaid cathode.

5. An electric discharge device of the magnetron type comprising aplurality .or enclosed electrodes including a cylindrical cathode and anannular anode structure substantially surrounding said cathode, meansfor establishing a magnetic field comprising a pole piece having a poleface positioned near said anode structure and having therein alongitudinally extending channel terminated at said pole face, saidchannel having a restricted section of a diameter substantially lessthan the transverse dimension of said cathode thereby controlling theconfiguration of the magnetic field to limit the divergence of theelectrons constituting the space discharge at the ends of the spacedischarge region defined by said cathode and a cooperating surface ofsaid anode structure.

6. An electric discharge device of the magnetron type comprising aplurality of enclosed electrodes including a cathode having an emittingsurface and an anode structure substantially surrounding said cathodeand having opposed end faces, means for establishing a magnetic eldcomprising a pole piece having a pole face substantially parallel to anend face of said anode structure, said pole piece having therein alongitudinal channel extending therethrough and terminating at the facethereof, and means extending through said channel supporting saidcathode, said channel having a restricted section in the vicinity ofsaid pole face, the diameter of said section being no greater than thediameter of said cathode to limit the magnetic ield distortion Withinthespace discharge region dened by said cathode and said anodestructure.

7. An electric discharge device of the magnetron type comprising aplurality of enclosed electrodes including a cathode having an emittingsurface and an 'anode structure substantially surrounding said cathodeand having vopposed end faces, means for establishing a magnetic fieldcomprising a pole piece having a pole face substantially parallel to anend face of said anode structure, said poler piece having a longitudinalchannel extending therethrough and terminated in the plane of said poleface, cathode supporting structure extending through said channel, saidchannel having a restricted section in the vicinity of said pole face,the diameter of said section being no greater than the diameter of saidcathode to minimize the magnetic field distortion within the spacedischarge region dened between said cathode and said anode structure,and an insulator within said channel maintaining said cathode supportingstructure in spaced relation thereto.

8. An electric discharge device of the magnetron type comprising aplurality of enclosed electrodes including a cathode having an emittingsurface and an anode structure substantially surrounding said cathode, apermanently magnetized pole piece having a face thereof substantiallyparallel to the plane of said anode structure and having therein alongitudinal channel extending therethrough and terminated at said face,cathode supporting structure extending through said channel, saidchannel having a restricted section in the vicinity of said pole face,

9. An electric discharge device of the magnetron type comprising aplurality of enclosed electrodes including a cylindrical thermioniccathode having an emitting surface and an annular anode structure havinga central opening within which said cathode risv located, said anodestructure having opposed end faces, a permanently magnetized pole piecehaving a pole `face substantially parallel to an end face of said anodestructure, a longitudinal channel extending through said pole piece andhaving a section in the vicinity of saidpole face, the diameter of saidsection being no greater than the diameter of said cathode to limit themagnetic eld distortion, cathode supporting structure extending throughsaid channel and asupporting insulator f for said cathode supportingstructure positioned within said channel and spaced from said restrctedsection.

RALPH J. BONDLEY.

